Lighting systems for illuminating liquid crystal displays employing light guides with edge lit end surfaces are known. These large area lighting systems generally do not have a uniform thickness, which is undesirable in many applications, such as back-lighting of liquid crystal displays (LCDs) for pagers, hand-held computers, organizers and the like. Examples of prior art light sources are described in the following patents:
U.S. Pat. No. 4,706,173 discloses a light reflecting apparatus that uses a lamp, probably a fluorescent lamp, with light impinging on a series of exterior reflective surfaces which reflect the light into an associated display.
U.S. Pat. No. 4,277,817 discloses two embodiments of a wedge-shaped body with a microgroove surface for emitting light from the grooved surface. The light is introduced in a direction that is generally parallel to the grooves.
U.S. Pat. No. 4,257,084 discloses a display that reflects light off an angled surface to strike a diffusing surface which has prismatic serration to extract the light.
U.S. Pat. No. 4,323,951 discloses a display having generally laminar light transmissive layers, one of which has a roughened back surface whereby light will be transmitted through a front surface of the laminar unit.
U.S. Pat. No. 4,528,617 discloses a light distribution apparatus that uses a transparent double wedge-shaped member having first internally reflecting surfaces to reflect a curtain of light to a second surface which has internally reflecting surfaces which reflect the light to an opposite surface for illuminating a generally rectangular area whereby to backlight an LCD display.
U.S. Pat. No. 5,050,946 discloses a light pipe that has a planar front surface for back-lighting LCDs. Light is injected into the light pipe from the ends. The back surface has a series of planar portions parallel to the front surface connected by facets, which are angled so that the injected light reflects internally off the facets through the front surface. A reflector having a planar, highly reflective, highly scattering surface or a sawtoothed or grooved reflecting surface is placed adjacent to facets.
U.S. Pat. No. 5,126,882 discloses a light pipe in which light emitted from a surface strikes a prism member which causes the light to be directed in a predetermined direction.
In copending application Ser. No. 08/095,753 filed Jul. 20, 1993, a flat panel display lighting system is disclosed wherein a thin, flat light guide has two spaced major surfaces with light introduced into one edge of the guide. Light is extracted from the light guide by being internally reflected from facets of a plurality of v-shaped microgrooves formed in one major surface.